The invention relates to monitoring processing of a substrate.
In substrate processing methods, features comprising semiconductor, dielectric, and conductor materials, including but not limited to, silicon, polysilicon, silicon dioxide, aluminum, copper and tungsten silicide materials, are formed on a substrate by, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), oxidation, nitridation, ion implantation, and etching processes. In CVD processes, a reactive gas is used to deposit material on the substrate. In PVD processes, a target is sputtered to deposit material on the substrate. In oxidation and nitridation processes, an oxide or nitride material, such as silicon dioxide or silicon nitride, is formed on the substrate by exposing the substrate to a suitable gaseous environment. In ion implantation, ions are implanted into the substrate. In conventional etching processes, etch-resistant features comprising resist or hard-mask, are formed on the substrate and the exposed portions of the substrate between the etch-resistant features (substrate open area) are etched to form patterns of gates, vias, contact holes or interconnect lines.
During processing of a substrate, a process monitoring method may be used to evaluate the progress of the process. The process monitoring methods may be used to stop or change the process, for example, after a pre-determined change occurs in a feature or material being processed, after a process stage, or at a process endpoint. For example, in the etching of trenches in a dielectric, such as silicon dioxide, on a silicon wafer, it may be desirable to stop etching after reaching a predetermined depth. In one conventional method, the peaks resulting from the constructive and destructive interference of radiation reflected from the substrate are counted to determine a substrate etching depth. However, it is difficult to accurately monitor the etching process when the substrate being etched has a small open area between the etch-resistant features because the process signal from such a region is small relative to the process signal from other portions of the substrate. Monitoring may be improved by detecting radiation reflected from the substrate that has been polarized at one or more angles relative to an orientation of a feature being processed on a substrate. The polarized radiation that is reflected from the substrate comprises components that are reflected from the features being etched on the substrate as well as components that are reflected from the etch resistant features, such as areas of the substrate covered by photoresist. By detecting and evaluating the intensities of the reflected radiation having different polarization states, the signal strength of the components of radiation reflected from features being etched on the substrate can be enhanced with respect to the components of radiation reflected from the etch-resistant features.
However, it is difficult to apply the radiation polarization and detection method to monitor the etching of more than one layer of material on the substrate when the indices of refraction are different for each layer of a number of stacked layers. The amplitude modulated signal resulting from the polarized radiation reflected from the substrate is dependent upon the index of refraction of both of the layers. As a result, the amplitude modulated signal obtained during etching of the upper layer is a complex function of the constructive and destructive interference of the polarized radiation reflected from both the upper and lower layer. Thus, the minima and maxima of the interference signal cannot be reliably counted to determine when a desired depth of a feature is etched in the second layer without knowing when the first layer has been etched through to reveal the second layer. This can make determination of the process endpoint difficult.
Thus, it is desirable to be able to determine the endpoint of an etch process comprising the etching of multiple layers on a substrate. It is further desirable to be able to determine when a first layer has been completely etched so that the etching of a second layer may be monitored.
A method of etching a substrate in a process zone and monitoring the etching process comprises (a) etching a substrate by placing the substrate in the process zone, providing an energized process gas in the process zone, and exhausting the process gas, whereby the energized gas may generate a radiation emission, (b) determining completion of a first stage of the etching process by detecting the intensities of one or more wavelengths of the radiation emission, generating a first signal in relation to the detected intensities, and evaluating the first signal, and (c) determining completion of a second stage of the etching process by detecting the intensities of one or more wavelengths of a polarized radiation reflected from the substrate being etched, generating a second signal in relation to the detected intensities, and evaluating the second signal.
A substrate etching apparatus comprises a chamber comprising a substrate support to receive a substrate, a gas inlet to introduce a process gas into the chamber, a gas energizer to energize the process gas to form an energized gas capable of etching the substrate and generating a radiation emission, and an exhaust to exhaust the process gas, one or more radiation detectors adapted to detect the intensities of one or more wavelengths of the radiation emission and generate a first signal in relation to the detected intensities, and detect the intensities of one or more wavelengths of polarized radiation reflected from the substrate being etched and generate a second signal in relation to the detected intensities, and a controller to evaluate the first signal to determine completion of a first stage of the etching process, and to evaluate the second signal to determine completion of a second stage of the etching process.
A method of etching a substrate in a process zone and monitoring the etching process comprises (a) etching a substrate by placing the substrate in the process zone, the substrate comprising a first layer and a second layer below the first layer, providing an energized process gas in the process zone, and exhausting the process gas, whereby the energized gas generates a radiation emission, (b) determining completion of etching of the first layer by detecting the intensities of one or more wavelengths of the radiation emission, generating a first signal in relation to the detected intensities, and evaluating the first signal to determine a change in the intensities of one or more wavelengths of the radiation emission that arises from etching of the second layer, and (c) monitoring the depth of etching of the second layer by detecting the intensities of one or more wavelengths of polarized radiation reflected from the substrate being etched, wherein the polarized radiation is polarized at one or more of a first polarization angle that is substantially parallel to an orientation of a feature being etched on the substrate and a second polarization angle that is substantially perpendicular to an orientation of a feature being etched on the substrate, generating a second signal in relation to the detected intensities, and evaluating the second signal.
A substrate etching apparatus adapted to etch a substrate comprising a first layer and a second layer below the first layer comprises a chamber comprising a substrate support to receive the substrate, a gas inlet to introduce a process gas into the chamber, a gas energizer to energize the process gas to form an energized gas capable of etching the substrate and generating a radiation emission, and an exhaust to exhaust the process gas, a radiation polarizer adapted to polarize a radiation at one or more of a first polarization angle that is substantially parallel to an orientation of a feature to be etched on the substrate, and a second polarization angle that is substantially perpendicular to an orientation of a feature to be etched on the substrate, one or more radiation detectors adapted to detect the intensities of one or more wavelengths of the radiation emission and generate a first signal in relation to the detected intensities, and detect the intensities of one or more wavelengths of the polarized radiation reflected from a surface of the substrate being etched and generate a second signal in relation to the detected intensities, and a controller adapted to evaluate the first signal to determine a change in the intensities of the one or more wavelengths of the radiation emission that arise during etching of the second layer, thereby determining completion of the first layer, and evaluate the second signal to monitor the depth of etching of the second layer.